1. Field of the Invention
The present invention relates to a control valve apparatus of seat valve type, and more particularly to a control valve apparatus suitable for a construction machine and a pressure circuit suitable for a hydraulic circuit of a construction machine.
2. Description of the Related Art
A control valve apparatus of seat valve type has hitherto been practiced as a combination of a seat-type main valve and a pilot control valve. The control valve apparatus is employed in a construction machine, for example, such that it is disposed in a joint portion of a main circuit between a pressure source and an actuator, or in a joint portion of a main circuit between an actuator and a reservoir, thereby controlling the speed and direction at and in which the actuator is moved. One example of such a control valve apparatus is disclosed in Patent Reference 1; JP,B 4-27401. In this disclosed control valve apparatus, a control pressure chamber is formed at the backside of a seat-type main valve to bias the main valve in the valve closing direction. The inlet side of the main valve and the control pressure chamber are communicated with each other via a variable throttle having an opening amount that is changed depending on the displacement of the main valve. Further, the control pressure chamber is communicated with the outlet side of the main valve via a pilot line, and a pilot valve is disposed in the pilot line. The displacement of the main valve is thus controlled depending on the displacement of the pilot valve.
FIG. 10 shows a known control valve apparatus of seat valve type. A housing 1 forms therein a circular valve seat 2 and a cylindrical wall 3 extending from the valve seat 2 in the axial direction. A valve member 4 is disposed within the cylindrical wall 3 and slides as a cylindrical plunger with respect to the cylindrical wall 3. A throttle is formed in a channel 5 inside the valve member 4 and serves as a variable throttle of which opening amount is increased as the distance from the valve seat 2 to the valve member 4 movable away from or closer to the valve seat 2 increases. The channel 5 is formed of at least one cutout or groove extending in the axial direction, for example, and is formed in an outer wall surface of the valve member 4. In the closed position of the valve member 4 shown in FIG. 10, an edge of the groove 5 located away from the valve seat 2 is positioned slightly outward of a stepped portion of the cylindrical wall 3 surrounding the valve member 4, i.e., an edge 6 of the cylindrical wall 3 farthest away from the valve seat 2. With such an arrangement, at all times, i.e., even when the valve member 4 abuts against the valve seat 2, a small passage portion 9 is formed between an inlet chamber 7 and a control pressure chamber 8 at the backside of the valve member 4. Therefore, the pressure in the control pressure chamber 8 becomes equal to the pressure in the inlet chamber 7 when a pilot control valve 10 is fully closed. When the pilot control valve 10 is operated to allow passage of a pilot flow, a pressurized medium (hydraulic fluid) flows through the throttle in the channel 5, whereupon the seat valve member 4 is moved away from the valve seat 2 by a distance that is required for establishing balance among the pressure in the control pressure chamber 8 formed at the backside of the seat valve member 4 to bias it in the valve closing direction, the pressure in the inlet chamber 7, and the pressure in an outlet chamber 11. The pilot control valve 10 acts as an adjustable throttle such that, as a pilot flow rate passing through the pilot control valve 10 increases, the seat valve member 4 is moved away from the valve seat 2 by a larger distance and a main flow rate passing through the seat valve is increased. Then, when the pilot control valve 10 is fully opened, the flow rate passing through the seat valve is maximized.
FIG. 11 shows another known control valve apparatus of seat valve type. In FIG. 11, the same components as those in FIG. 10 are denoted by the same symbols. This control valve apparatus differs from that shown in FIG. 10 in positions of the inlet chamber 7 and the outlet chamber 11 and in shape of the channel 5, but it operates in the same manner as the control valve apparatus of FIG. 10.
In the related art described above, because the pilot flow rate passing through the pilot control valve 10 is a small part of the total flow rate, the pilot control valve 10 can be controlled by a small force. Accordingly, it is easy to remotely control the valve by using, e.g., an electric signal.